Composition and process for metallizing nonconductive plastic surfaces

ABSTRACT

The present invention relates to a composition of an etching solution and a process for metallizing electrically nonconductive plastic surfaces of articles using the etching solution. The etching solution is based on a stabilized acidic permanganate solution. After the treatment with the etching solution, the articles can be metallized.

The present application is a U.S. National Stage Application based onand claiming benefit and priority under 35 U.S.C. § 371 of InternationalApplication No. PCT/EP2015/056195, filed 24 Mar. 2015, which in turnclaims benefit of and priority to European Application No. 14163083.0filed 1 Apr. 2014, the entirety of both of which is hereby incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a composition of an etching solutionand a process for metallizing electrically nonconductive plasticsurfaces of articles using the etching solution. The etching solution isbased on a stabilized acidic permanganate solution. After the treatmentwith the etching solution, the articles can be metallized.

BACKGROUND OF THE INVENTION

Articles made from electrically nonconductive plastic can be metallizedby an electroless metallization process or alternatively by a directelectroplating process. In both processes, the article is first cleanedand etched. The etching is typically undertaken by means ofchromosulphuric acid. The etching serves to make the surface of thearticle receptive to the subsequent metallization, such that thesurfaces of the articles are well-wetted with the respective solutionsin the subsequent treatment steps and the deposited metal ultimately hassufficiently firm adhesion on the surface.

After etching, the plastic is activated for the electrolessmetallization by means of an activator comprising a noble metal, andthen metallized electrolessly. Subsequently, a thicker metal layer canalso be applied electrolytically. In the case of the directelectroplating process, which does not need an electrolessmetallization, the etched surface is typically treated with a palladiumcolloid solution. Subsequently, the surface is contacted with analkaline solution comprising copper ions complexed with a complexingagent to increase the conductivity. This step leads to the formation ofa copper layer and hence to a metal layer on the surface of the articlewith elevated conductivity. Thereafter, the article can be directlyelectrolytically metallized (EP 1 054 081 B1).

A further possibility to provide a sufficient electrically conductivelayer on the etched surface is to treat it with a metal ion solution andafterwards with a sulphide solution. These two treatment steps generatean electrically conductive metalsulfide layer on the etched surfaceprior to metallizing it by direct electroplating (EP 1 0010 52 A2).

As etching solutions based on chromosulphuric acid are toxic, theliterature describes attempts to replace it with etching solutionscomprising permanganate salts.

EP 202 57 08 A1 discloses a pickling solution and a pickling process forpickling ABS plastic surfaces or ABS polymer blend surfaces prior to asubsequent metallization of these surfaces. The pickling solutionincludes Mn(VII) ions and an inorganic acid. The pickling solution isfree of alkali and alkaline earth ions which is achieved by generatingthe Mn(VII) ions by anodic oxidation of manganese(II) salts. Redoxmediators like Ag (I), Bi(V), V(V), Mo(VI), Cu(II), Ti(II), Au(I),Fe(II), Ce(III), or Sb(II) ions may be added in order to increase theefficiency of the anodic oxidation. The absence of alkali metalpermanganate compounds overcomes the problem of rapid self-decompositionof the acidic permanganate solution. The pickling solution of EP 202 5708 has the disadvantages that it is laborious to prepare and the educts,the manganese(II) salts, are expensive as they have to be free of alkaliand earth alkali metal ions. The pickling process and the metallizationprocess including the pickling require additional equipment whichrenders the processes and the respective process lines even moreexpensive and laborious.

Although acidic permanganate solutions can be suited for etchingplastics surfaces and sufficient adhesion strength between depositedmetal layer and plastic substrate may be obtained, acidic permanganatesolutions are unstable. When etching the substrate surface, thepermanganate ions are reduced and the end-product is manganese dioxide.Manganese dioxide catalyzes the formation of further manganese dioxideand oxygen and leads to self-decomposition of permanganate. Thus, theetching effect of a freshly prepared acidic permanganate solution willbe insufficient already after several hours. The acidic permanganateetching solution can be re-sharpened by addition of permanganate whichcauses a high consumption of the permanganate compounds. In addition,the concentration of manganese dioxide further increases. Moreover,manganese dioxide forms a precipitate that is difficult to remove fromthe etching solution. As a result of this enrichment the viscosity ofthe etching solution will be increased up to a point where the etchingsolution must be discarded, because satisfying etching results cannot beachieved any longer. Further, the precipitate spreads over the entiremetallizing process of the plastic surfaces and impairs the metaldeposition, so that faulty or other-wise insufficient metal layers arefinally deposited. A constant high quality of the metallizationtherefore cannot be achieved.

OBJECTIVE OF THE PRESENT INVENTION

Therefore, the objective of the present invention is to provide astable, acidic permanganate solution that is easy to prepare, has a longlife and minimizes permanganate consumption.

A further objective was to provide a method for etching electricallynonconductive plastic surfaces having a sufficient etching effect.

Another objective was to provide a method for metallizing electricallynonconductive plastic surfaces of articles with constant high quality ofthe metallization and sufficient adhesion strength of the metal layerdeposited onto the plastic surfaces.

SUMMARY OF THE INVENTION

These objectives are achieved by the following solution and processes.

An etching solution for treating nonconductive plastic surfaces,comprising

-   -   (i) at least one acid,        -   wherein the concentration of the at least one acid ranges            from 0.02-0.6 mol/l based on a monobasic acid; and    -   (ii) at least one permanganate salt selected from alkali metal        permanganates and earth alkali metal permanganates,        -   wherein the permanganate salt is present in the etching            solution in a concentration between 30 g/l and 250 g/l; and    -   (iii) at least one source for a metal ion, wherein the metal of        the metal ion is selected from titanium, zirconium, niobium,        molybdenum, ruthenium, rhodium, nickel, copper, silver, zinc and        cadmium.

The metal ion according to (iii) stabilizes the etching solution. Thatmeans the presence of metal ions according to (iii) prevents theself-decomposition of the acidic etching solution containing alkalimetal permanganates and earth alkali metal permanganates.

A process for etching electrically nonconductive plastic surfaces ofarticles, comprising the process step of:

A) treating the plastic surface with at least one etching solution fortreating nonconductive plastic surfaces, the etching solution comprising

-   -   (i) at least one acid,    -   (ii) at least one permanganate salt selected from alkali metal        permanganates and earth alkali metal permanganates, and    -   (iii) at least one source for a metal ion, wherein the metal of        the metal ion is selected from titanium, zirconium, niobium,        molybdenum, ruthenium, rhodium, nickel, copper, silver, zinc and        cadmium.

Using the above described etching solution in an etching process leadsto sufficiently etched, electrically nonconductive plastic surfaces.

A process for metallizing electrically nonconductive plastic surfaces ofarticles, comprising the process steps of:

A) treating the plastic surface with at least one etching solution fortreating nonconductive plastic surfaces, the etching solution comprising

-   -   (i) at least one acid,    -   (ii) at least one permanganate salt selected from alkali metal        permanganates and earth alkali metal permanganates, and    -   (iii) at least one source for a metal ion, wherein the metal of        the metal ion is selected from titanium, zirconium, niobium,        molybdenum, ruthenium, rhodium, nickel, copper, silver, zinc and        cadmium, and        B) metallizing the plastic surface with a metallizing solution.

Using the above described etching solution in a metallizing processleads to metal deposits without surface defects and sufficient adhesionstrength of the metal layer deposited onto the plastic surfaces.

DESCRIPTION OF THE DRAWINGS

FIG. 1: Evolution of oxygen in a comparative acidic permanganatesolution containing no metal ions according to (iii).

FIG. 2: Evolution of oxygen in an inventive acidic permanganate solutioncontaining metal ions according to (iii).

FIG. 3: Evolution of oxygen in solutions containing varyingconcentrations of permanganate in absence or presence of metal ionsaccording to (iii).

FIG. 4: Evolution of oxygen in comparative acidic permanganate solutionscontaining metal ions different from metal ions according to (iii)

DETAILED DESCRIPTION OF THE INVENTION

The inventive etching solution comprises at least one acid, at least onepermanganate salt selected from alkali metal permanganates and earthalkali metal permanganates, and at least one source for a metal ionaccording to (iii).

The alkali metal permanganates are selected from the group comprisingpotassium permanganate, sodium permanganate, lithium permanganate andrubidium permanganate, preferably potassium permanganate and sodiumpermanganate. The earth alkali metal permanganates are selected from thegroup comprising magnesium permanganate and calcium permanganate,preferably calcium permanganate. The permanganate salt is present in theetching solution in a concentration between 30 g/l and 250 g/l,preferably between 30 g/l and 180 g/l, more preferably between 90 g/land 180 g/l. Owing to its solubility, potassium permanganate may bepresent in the etching solution in a concentration of up to 70 g/l.Sodium permanganate may be present in the etching solution in aconcentration of up to 250 g/l. The lower concentration limit for eachof these two salts is typically 30 g/l. The content of sodiumpermanganate is preferably between 90 g/l and 180 g/l.

In a further embodiment of the present invention the concentration ofthe permanganate salt may be even lower. In this embodiment theconcentration of the permanganate salt preferably ranges from 5 g/l to250 g/l, more preferably from 10 g/l to 180 g/l, most preferably from 15g/l to 150 g/l.

The etching solution is acidic, meaning that it contains at least oneacid according to (i). Acids which are used in the etching solution arepreferably inorganic acids. The inorganic acid in the etching solutionis selected from the group comprising sulphuric acid, nitric acid andphosphoric acid. The acid concentration is low as this contributesfurther to the stability of the etching solution. The acid concentrationis between 0.02-0.6 mol/l based on a monobasic acid. It is preferablybetween 0.06 and 0.45 mol/l, more preferably between 0.07 and 0.30mol/l, based in each case on a monobasic acid. Preference is given tousing sulphuric acid in a concentration between 0.035 and 0.15 mol/l,corresponding to an acid concentration between 0.07 and 0.30 mol/l basedon a monobasic acid. The permanganate salt and the acid of the etchingsolution of the present invention contribute to the stability of theetching solution if contained in the concentration ranges specifiedabove. An acidic permanganate solution is very reactive. The oxidationreaction with the plastic surface then forms many manganese(IV) specieswhich precipitate out. These manganese(IV) species are predominantlymanganese(IV) oxides or oxide hydrates and are referred to hereinaftersimply as manganese dioxide. The manganese dioxide precipitate has adisruptive effect on the subsequent metallization if it remains on theplastic surface. The manganese dioxide also catalyses the reaction ofpermanganate with water according to formula (2) and thus leads toinstability of an etching solution.4MnO4⁻+2H₂O→4MnO₂+3O₂+4OH⁻  Formula (2):

Etching solutions should therefore advantageously be kept free ofmanganese dioxide. It has been found that, surprisingly, the formationof manganese dioxide species which are difficult to remove is noticeablydecreased when metal ions according to (iii) are present in an acidicpermanganate etching solution.

The metal of the metal ion according to (iii) is selected from titanium,zirconium, niobium, molybdenum, ruthenium, rhodium, nickel, copper,silver, zinc and cadmium.

Preferably, the metal may be selected from copper, nickel, and zinc.More preferably, the metal may be selected from copper.

The at least one source for a metal ion according to (iii) is selectedfrom water soluble salts of the above listed metals of the metal ionaccording to (iii). Preferably, the at least one source for a metal ionis selected from water soluble sulphate, phosphate, nitrate andpermanganate salts of the above listed metals of the metal ion. Morepreferably, the at least one source for a metal ion is selected fromcopper sulfate, copper phosphate, copper nitrate, copper permanganate,silver nitrate, zinc sulphate, zinc nitrate, zinc permanganate, cadmiumsulphate, cadmium nitrate, titanium sulfate, titanium nitrate, zirconiumsulfate, nickel sulfate, nickel nitrate, rhodium sulphate and thehydrates thereof. Most preferably, the at least one source for a metalion is selected from copper sulfate, copper phosphate, copper nitrate,copper permanganate and the hydrates thereof. The concentration of themetal ion according to (iii) ranges from 1 mmol/l to 1 mol/l, preferablyfrom 10 mmol/l to 1 mol/l, more preferably from 10 mmol/l to 100 mmol/l,most preferably 30 mmol/l to 100 mmol/l.

In a further embodiment of the present invention the concentration ofthe metal ion according to (iii) ranges preferably from 1 mmol/l to 90mmol/l, more preferably from 1 mmol/l to 80 mmol/l.

The molar ratio of permanganate ions according to (ii) to metal ionsaccording to (iii) ranges from 5:1 to 40:1, preferably from 10:1 to20:1.

The steps in the processes of the present invention are performed in thesequence specified, but not necessarily in immediate succession. It ispossible for further process steps and additionally rinse steps in eachcase, preferably with water, to be performed between the steps.

The inventive process for etching electrically nonconductive plasticsurfaces of articles, comprises the process step of:

A) treating the plastic surface with at least one etching solution fortreating nonconductive plastic surfaces, the etching solution comprising

-   -   (i) at least one acid,    -   (ii) at least one permanganate salt selected from alkali metal        permanganates and earth alkali metal permanganates, and    -   (iii) at least one source for a metal ion, wherein the metal of        the metal ion is selected from titanium, zirconium, niobium,        molybdenum, ruthenium, rhodium, nickel, copper, silver, zinc and        cadmium.

The etching solution can be employed at temperatures between 30° C. and90° C., preferably between 55° C. and 75° C., most preferably between65° C. and 72° C.

The optimal treatment time depends on the plastic surface being treatedand the selected temperature of the etching solution. For ABS and ABS/PCplastic surfaces, the best adhesion strength between plastic surface andsubsequently applied metal layer is achieved at a treatment time between5 and 30 minutes, preferably between 10 and 25 minutes and morepreferably between 10 and 15 minutes. A longer treatment time than 30minutes generally leads to no further improvement in the adhesionstrengths.

The electrically nonconductive plastic surfaces have been manufacturedfrom at least one electrically nonconductive plastic. In one embodimentof the present invention, the at least one electrically nonconductiveplastic is selected from the group comprising anacrylonitrile-butadiene-styrene copolymer (ABS copolymer), a polyamide(PA), a polycarbonate (PC) and a mixture of an ABS copolymer with atleast one further polymer.

In a preferred embodiment of the invention, the electricallynonconductive plastic is an ABS copolymer or a mixture of an ABScopolymer with at least one further polymer. The at least one furtherpolymer is more preferably polycarbonate (PC), which means thatparticular preference is given to ABS/PC mixtures.

The inventive process for metallizing electrically nonconductive plasticsurfaces of articles, comprises the process steps of:

A) treating the plastic surface with at least the etching solution fortreating nonconductive plastic surfaces, the etching solution comprising

-   -   (i) at least one acid,    -   (ii) at least one permanganate salt selected from alkali metal        permanganates and earth alkali metal permanganates, and    -   (iii) at least one source for a metal ion, wherein the metal of        the metal ion is selected from titanium, zirconium, niobium,        molybdenum, ruthenium, rhodium, nickel, copper, silver, zinc and        cadmium, and        B) metallizing the plastic surface with a metallizing solution.

Process step A) is performed as described for the process for etchingelectrically nonconductive plastic surfaces above.

In a preferred embodiment of the invention, process step A) is precededby performance of the following further process step:

pretreatment step: treating the plastic surface in an aqueous solutioncomprising at least one glycol compound.

This further process step is referred to hereinafter as pretreatmentstep. This pretreatment step increases the adhesion strength between theplastic and the metal layer.

A glycol compound is understood to mean compounds of the followinggeneral formula (I):

whereinn is an integer from 1 to 4; andR1 and R2 are each independently —H, —CH3, —CH2-CH3, —CH2-CH2-CH3,—CH(CH3)-CH3, —CH2-CH2-CH2-CH3, —CH(CH3)-CH2-CH3, —CH2-CH(CH3)-CH3,—CH2-CH2-CH2-CH2-CH3, —CH(CH3)-CH2-CH2-CH3, —CH2-CH(CH3)-CH2-CH3,—CH2-CH2-CH(CH3)-CH3, —CH(CH2-CH3)-CH2-CH3, —CH2-CH(CH2-CH3)-CH3,—CO—CH3, —CO—CH2-CH3, —CO—CH2-CH2-CH3, —CO—CH(CH3)-CH3,—CO—CH(CH3)-CH2-CH3, —CO—CH2-CH(CH3)-CH3, —CO—CH2-CH2-CH2-CH3.

According to the general formula (I), the glycol compounds include theglycols themselves and glycol derivatives. The glycol derivativesinclude the glycol ethers, the glycol esters and the glycol etheresters. The glycol compounds are solvents.

Preferred glycol compounds are ethylene glycol, diethylene glycol,ethylene glycol monomethyl ether acetate, ethylene glycol monoethylether acetate, ethylene glycol monopropyl ether acetate, ethylene glycolacetate, diethylene glycol monoethyl ether acetate, diethylene glycolmonomethyl ether acetate, diethylene glycol monopropyl ether acetate,butyl glycol, ethylene glycol monobutyl ether, ethylene glycol diacetateand mixtures thereof. Particular preference is given to diethyleneglycol monoethyl ether acetate, ethylene glycol acetate, ethylene glycoldiacetate, butyl glycol and mixtures thereof.

In the case of use of glycol esters and glycol ether esters, it isadvisable to keep the pH of the aqueous solution of the glycol compoundwithin the neutral range by suitable measures, in order to as far aspossible suppress the hydrolysis to give the alcohol and carboxylicacid. One example is the hydrolysis of the diethylene glycol monoethylether acetate:CH3-CO—O—CH2CH2-O—CH2CH2-O—CH2CH3+H₂O→CH3-COOH+HO—CH2CH2-O—CH2CH2-O—CH2CH3

The solution of a glycol ester or glycol ether ester contains a pHbuffering agent thus to keep it within the neutral pH range, which meansscavenging the protons obtained by hydrolysis of the solvent. Aphosphate buffer mixture has been found to be sufficiently suitable forthis purpose. The readily soluble potassium phosphates allowsufficiently high concentrations with good buffer capacity at solventconcentrations up to 40% by vol.

The optimal treatment time for the plastic surface depends on theplastic used, the temperature, and the nature and concentration of theglycol compound. Treating the plastic surface in an aqueous solutioncomprising at least one glycol compound contributes to the adhesionstrength of the subsequently deposited metal layer. The treatment timein the pretreatment step is between 1 and 30 minutes, preferably between5 and 20 minutes and more preferably between 7 and 15 minutes.

The treatment temperature is between 20° C. and 70° C., depending on thenature of the solvent or solvent mixture used. Preference is given to atreatment temperature between 20° C. and 50° C., particular preferenceto a treatment temperature between 20° C. and 45° C.

The treatment of the plastic surfaces in the pretreatment step can beperformed in an aqueous solution comprising one glycol compound or in anaqueous solution comprising two or more different glycol compounds. Thetotal concentration of glycol compounds in the aqueous solution is 5% byvol.-50% by vol., preferably 10% by vol.-40% by vol. and more preferably20% by vol.-40% by vol. If said solution contains one glycol compound,the overall concentration corresponds to the concentration of this oneglycol compound. If said solution contains two or more different glycolcompounds, the total concentration corresponds to the sum total of theconcentrations of all glycol compounds present. In the context of thesolution containing at least one glycol compound, the concentrationfigures for the glycol compound/glycol compounds in % are alwaysunderstood to mean a concentration in % by vol.

In a preferred embodiment of the invention, following further processstep is performed after process step A):

A i) treating the plastic surface with an alkaline etching solution.

Process step A i) may be performed in the process for etchingelectrically nonconductive plastic surfaces of articles and/or in theprocess for metallizing electrically nonconductive plastic surfaces ofarticles. If the process for metallizing electrically nonconductiveplastic surfaces is performed including process step B), process step Ai) is preferably performed after process step A) and prior to processstep B). Preferably, process step A i) is performed between processsteps A) and B).

The alkaline etching solution comprises:

-   1. at least one permanganate salt selected from alkali metal    permanganates and earth alkali metal permanganates and-   2. a hydroxide ion source.

The permanganate salts of the alkaline etching solution are selectedfrom the same permanganate salts as listed for the acidic etchingsolution; these are the permanganate salts according to (ii). Thepermanganate salt is selected independently for the alkaline and acidicetching solutions, meaning that the two etching solutions may containthe same permanganate salt or the two etching solutions may containdifferent permanganate salts.

The permanganate salt is present in alkaline etching solution in aconcentration as given above for the acidic etching solution. Theconcentration of the permanganate salt for the alkaline and acidicetching solutions is selected independently, meaning that the twoetching solutions may contain the same concentration of permanganatesalt or the two etching solutions may contain different concentrationsof permanganate salts.

The hydroxide ion source in the alkaline etching solution is selectedfrom the group of alkali metal hydroxides comprising sodium hydroxide,potassium hydroxide and lithium hydroxide. The hydroxide ion source ispreferably sodium hydroxide. The hydroxide ion source in the alkalineetching solution is selected independently of the metal permanganate,meaning that the alkaline etching solution may comprise a hydroxide ionsource and metal permanganate with the same alkali metal ion, or thealkaline etching solution may comprise a hydroxide ion source and metalpermanganate with different alkali metal ions.

The concentration of the hydroxide ion source is between 1 g/l and 100g/l, preferably between 5 g/l and 50 g/l and more preferably between 10g/l and 30 g/l.

The alkaline etching solution can be employed at temperatures between20° C. and 90° C., preferably between 30° C. and 75° C. and morepreferably between 30° C. and 60° C. The treatment of the plasticsurfaces with alkaline etching solution within the temperature rangebetween 30° C. and 60° C. leads to higher adhesion strengths. Thestability of the alkaline permanganate solution falls somewhat atelevated temperatures. In general, however, the alkaline permanganatesolution is much more stable than the acidic permanganate solution. Thestability of the alkaline permanganate solution is uncritical within therange between 40° C. and 60° C.

The optimal treatment time with the alkaline etching solution likewisedepends on the plastic surface being treated and the selectedtemperature of an etching solution. Treatment time with the alkalineetching solution ranges between 1 and 20 minutes, preferably between 1and 15 minutes and more preferably between 1 and 5 minutes. A longertreatment time than 20 minutes generally does not lead to any furtherimprovement in the adhesion strengths.

In a preferred embodiment of the invention, following further processstep is performed after process step A):

-   A ii) treating the plastic surface in a solution comprising a    reducing agent for manganese dioxide.

The further process step A ii) is also referred to as reductiontreatment. This reduction treatment reduces manganese dioxide adheringto the plastic surfaces to water-soluble manganese(II) ions. Thereduction treatment is conducted optionally after A i). Process step Aii) may be performed in the process for etching electricallynonconductive plastic surfaces of articles and/or in the process formetallizing electrically nonconductive plastic surfaces of articles. Ifthe process for metallizing electrically nonconductive plastic surfacesis performed including process step B), process step A ii) is preferablyperformed after process step A) and prior to process step B); morepreferably after process step A i) and prior to process step B).Preferably, process step A ii) is performed between process steps A) andB).

For this purpose, an acidic solution of a reducing agent is used. Thereducing agent is selected from the group comprising hydroxylammoniumsulphate, hydroxylammonium chloride and hydrogen peroxide. Preference isgiven to an acidic solution of hydrogen peroxide because hydrogenperoxide is neither toxic nor complex-forming. The content of hydrogenperoxide in the solution of the reduction treatment (reduction solution)is between 25 ml/l and 35 ml/l of a 30% hydrogen peroxide solution (% byweight), preferably 30 ml/l of a 30% hydrogen peroxide solution (% byweight).

The acid used in the reduction solution is an inorganic acid, preferablysulphuric acid. The acid concentration is 0.5 mol/l to 5.0 mol/l,preferably 1.0 mol/l to 3.0 mol/l, more preferably 1.0 mol/l to 2.0mol/l, based in each case on a monobasic acid. In the case of use ofsulphuric acid, particular preference is given to concentrations of 50g/l 96% sulphuric acid to 100 g/l 96% sulphuric acid, corresponding toan acid concentration of 1.0 mol/l to 2.0 mol/l based on a monobasicacid.

The reduction treatment in process step A ii) is performed at atemperature between 30° C. and 50° C., preferably at 40° C. to 45° C.The reduction treatment is performed for a period between 0.5 and 10minutes, preferably between 1 and 6 minutes, more preferably between 3and 6 minutes. In order to achieve sufficient protection of the racksprior to activation, it is advantageous to increase the treatment timein the reduction solution to 3 to 10 minutes, preferably to 3 to 6minutes.

In a preferred embodiment of the invention, the etched plastics surfaceis metallized by electroless metal plating.

In this embodiment the process of the present invention furthercomprises process step A iii), in which a plastic surface is treatedwith a solution of a metal colloid or of a compound of a metal.

The metal of the metal colloid or of the metal compound is selected fromthe group comprising the metals of transition group I of the PeriodicTable of the Elements (PTE) and transition group VIII of the PTE.

The metal of transition group VIII of the PTE is selected from the groupcomprising palladium, platinum, iridium, rhodium and a mixture of two ormore of these metals. The metal of transition group I of the PTE isselected from the group comprising gold, silver and a mixture of thesemetals.

A preferred metal in the metal colloid is palladium. The metal colloidis stabilized with the protective colloid. The protective colloid isselected from the group comprising metallic protective colloids, organicprotective colloids and other protective colloids. As a metallicprotective colloid, preference is given to tin ions. The organicprotective colloid is selected from the group comprising polyvinylalcohol, polyvinylpyrrolidone and gelatine, preferably polyvinylalcohol.

In a preferred embodiment of the invention, the solution of the metalcolloid in process step A iii) is an activator solution with apalladium/tin colloid. This colloid solution is obtained from apalladium salt, a tin(II) salt and an inorganic acid. A preferredpalladium salt is palladium chloride. A preferred tin(II) salt istin(II) chloride. The inorganic acid may consist in hydrochloric acid orsulphuric acid, preferably hydrochloric acid. The colloid solution formsthrough reduction of the palladium chloride to palladium with the aid ofthe tin(II) chloride. The conversion of the palladium chloride to thecolloid is complete; therefore, the colloid solution no longer containsany palladium chloride.

If, in the subsequent process steps, the plastic surfaces are metallizedelectrolessly, the concentration of palladium in the colloid solution is5 mg/l-100 mg/l, preferably 20 mg/l-50 mg/l and more preferably 30mg/l-45 mg/l, based on Pd²⁺.

If the plastic surfaces in the subsequent process steps are metallizedby means of direct electroplating, the concentration of palladium in thecolloid solution is 50 mg/l-200 mg/l, preferably 75 mg/l-150 mg/l, morepreferably 100 mg/l-150 mg/l, and more preferably 80 mg/l-120 mg/l,based on Pd²⁺.

The concentration of tin(II) chloride is 0.5 g/l-10 g/l, preferably 1g/l-5 g/l and more preferably 2 g/l-4 g/l, based on Sn²⁺. Theconcentration of hydrochloric acid is 100 ml/l-300 ml/l (37% by weightof HCl). In addition, a palladium/tin colloid solution additionallycomprises tin(IV) ions which form through oxidation of the tin(II) ions.The temperature of the colloid solution during process step B) is 20°C.-50° C. and preferably 35° C.-45° C. The treatment time with theactivator solution is 0.5 min-10 min, preferably 2 min-5 min and morepreferably 3 min-5 min.

In a further embodiment of the invention, in process step A iii), thesolution of a compound of a metal is used in place of the metal colloid.The solution of a metal compound used is a solution comprising an acidand a metal salt. The metal in the metal salt consists in one or more ofthe above-listed metals of transition groups I and VIII of the PTE. Themetal salt may be a palladium salt, preferably palladium chloride,palladium sulphate or palladium acetate, or a silver salt, preferablysilver acetate. The acid is preferably hydrochloric acid. Alternatively,it is also possible to use a metal complex, for example a palladiumcomplex salt, such as a salt of a palladium-aminopyridine complex. Themetal compound in process step A iii) is present in a concentration of40 mg/l to 80 mg/l, based on the metal. The solution of the metalcompound can be employed at a temperature of 25° C. to 70° C.,preferably at 25° C. The treatment time with the solution of a metalcompound is 0.5 min-10 min, preferably 2 min-6 min and more preferably 3min-5 min.

Prior to process step Aiii), the following further process step can beperformed: Rack protection: treating the plastic surface with a solutioncomprising iodate ions.

The rack protection step leads to protection of the plastic casing ofthe racks against metal deposition while the plastic articles which arefastened to the racks are being metallized.

The protection of the rack is executed at a temperature of 20° C. to 70°C., more preferably of 45° C. to 55° C. The iodate ions are in the formof metal iodates. The metal iodates are selected from the groupcomprising sodium iodate, potassium iodate, magnesium iodate, calciumiodate and the hydrates thereof. The concentration of the metal iodatesis between 5 g/l and 50 g/l, preferably from 15 g/l to 25 g/l. Theduration of the treatment of the rack with iodate ions is between 1 and20 minutes, preferably between 2 and 15 minutes and more preferablybetween 5 and 10 minutes.

The solution comprising iodate ions may further comprise an acid.Inorganic acids are preferred. The inorganic acids are selected from thegroup comprising sulphuric acid and phosphoric acid, preferablysulphuric acid. The acid concentration is 0.02 mol/l to 2.0 mol/l,preferably 0.06 mol/l to 1.5 mol/l, more preferably 0.1 mol/l to 1.0mol/l, based in each case on a monobasic acid. In the case of use ofsulphuric acid, particular preference is given to concentrations of 5g/l 96% sulphuric acid to 50 g/l 96% sulphuric acid, corresponding to anacid concentration of 0.1 mol/l to 1.0 mol/l based on a monobasic acid.

Between process steps A ii) and Aiii), the following further processstep can be performed:

preliminary dipping: treating the plastic surface in an aqueous acidicsolution.

The aqueous acidic solution used in the preliminary dipping step isreferred to as a preliminary dipping solution. The preliminary dippingsolution has the same composition as the colloid solution in processstep B), without the presence of the metal in the colloid and theprotective colloid thereof. The preliminary dipping solution, in thecase of use of a palladium/tin colloid solution in process step A iii),comprises exclusively hydrochloric acid if the colloid solution likewisecomprises hydrochloric acid. For preliminary dipping, brief immersioninto the preliminary dipping solution at ambient temperature issufficient. Without rinsing the plastic surfaces, they are treatedfurther directly with the colloid solution of process step B) after thetreatment in the preliminary dipping solution.

The preliminary dipping step is preferably performed when process step Aiii) involves the treatment of a plastic surface with a solution of ametal colloid. The preliminary dipping step can also be performed whenprocess step A iii) involves the treatment of a plastic surface with asolution of a compound of a metal.

In the embodiment including electroless metal plating, the followingfurther process steps may be performed between process steps A iii) andB):

A iv) treating the plastic surface in an aqueous acidic solution and

A v) electrolessly metallizing the plastic surface in a metallizingsolution.

These further process steps A iv) and A v) are employed when thearticles are to be metallized by an electroless metallization process,i.e. a first metal layer is to be applied to the plastic surfaces by anelectroless process.

If the activation in process step A iii) has been performed with a metalcolloid, the plastic surfaces are treated in process step A iv) with anaccelerator solution in order to remove constituents of the colloid inthe colloid solution, for example a protective colloid, from the plasticsurfaces. If the colloid in the colloid solution in process step A iii)is a palladium/tin colloid, the accelerator solution used is preferablyan aqueous solution of an acid. The acid is selected, for example, fromthe group comprising sulphuric acid, hydrochloric acid, citric acid andtetrafluoroboric acid. In the case of a palladium/tin colloid, theaccelerator solution helps to remove the tin compounds which served asthe protective colloid.

Alternatively, in process step A iv), a reductor treatment is performedwhen, in process step A iii), a solution of a metal compound has beenused in place of a metal colloid for the activation. The reductorsolution used for this purpose then comprises, if the solution of themetal compound was a hydrochloric acid solution of palladium chloride oran acidic solution of a silver salt, hydrochloric acid and tin(II)chloride. The reductor solution may also comprise another reducingagent, such as NaH₂PO₂ or else a borane or borohydride, such as analkali metal borane or alkaline earth metal borane ordimethylaminoborane. Preference is given to using NaH₂PO₂ in thereductor solution.

Process step A iv) and optionally one or more rinse steps are followedby process step A v) in which the plastic surfaces are metallizedelectrolessly. Electroless nickel-plating is accomplished, for example,using a conventional nickel bath which comprises, inter alia, nickelsulphate, a hypophosphite, for example sodium hypophosphite, as areducing agent, and also organic complexing agents and pH adjusters (forexample a buffer). The reducing agent used may likewise bedimethylaminoborane or a mixture of hypophosphite anddimethylaminoborane.

Alternatively, it is possible to use an electroless copper bath forelectroless copper-plating, the electroless copper bath typicallycomprising a copper salt, for example copper sulphate or copperhypophosphite, and also a reducing agent, such as formaldehyde or ahypophosphite salt, for example an alkali metal or ammonium salt, orhypophosphorous acid, and additionally one or more complexing agentssuch as tartaric acid, and also a pH adjuster such as sodium hydroxide.

The surface thus rendered conductive can subsequently beelectrolytically further metallized in order to obtain a functional ordecorative surface.

In a further embodiment of the invention, the plastic surfaces aremetallized by means of direct electroplating, meaning that the plasticsurfaces are metallized not electrolessly but directly by anelectrolytic metallization process. In this embodiment, the followingfurther process step is performed between process steps A) and B):

A iv) treating the plastic surfaces in a conversion solution.

Preferably process step A iv) is performed between process steps A iii)and B). This step A iv) is an alternative process step. It replacessteps A iv) and A v) of the embodiment in which the etched plasticssurface is metallized by electroless metal plating. The remainingprocess steps are identical for the embodiment concerning electrolessmetal plating and for the embodiment concerning direct electroplating.

The effect of the treatment of the plastic surfaces in a conversionsolution is that an electrically conductive layer sufficient for adirect electrolytic metallization is formed on the plastic surfaceswithout prior electroless metallization. If the colloid in the colloidsolution in process step A iii) is a palladium/tin colloid, theconversion solution used is preferably an alkaline solution of copperions complexed by a complexing agent. For example, the conversionsolution may comprise an organic complexing agent, such as tartaricacid, ethylenediaminetetraacetic acid (EDTA) or ethanolamine and/or asalt thereof, and a copper salt, such as copper sulphate.

The conversion solution may comprise (a) a soluble metal salt, (b) agroup IA metal hydroxide, and (c) a complexing agent for an ion of themetal of the soluble metal salt according to (a). The metal of thesoluble metal salt according to (a) may be selected from the groupcomprising Cu, Ag, Au, Ni and mixtures thereof. The soluble metal saltaccording to (a) may be selected from the group comprising Ag(I),Ag(II), Au(I), Au(II), Ni(II) and Cu(II) salts. Preferably, the solublemetal salt according to (a) may be a Cu(II) salt. The soluble metal saltaccording to (a) may be present in the conversion solution in aconcentration ranging from 0.2 mmol/l to 200 mmol/l, preferably from 1mmol/l to 100 mmol/l, more preferably from 5 mmol/l to 20 mmol/l.

The metal of the group IA metal hydroxide according to (b) may beselected from the group comprising Li, Na, K, Rb, Cs and mixturesthereof, preferably Li, Na, K and mixtures thereof. The group IA metalhydroxide according to (b) may be present in the conversion solution ina concentration ranging from 0.05 mol/l to 5 mol/l, preferably from 0.1mol/l to 3 mol/l, more preferably from 0.5 mol/l to 2 mol/l.

The complexing agent according to (c) may be selected from the groupcomprising mono and poly carboxylic acids, like tartaric acid, gluconicacid, lactic acid, acetic acid, succinic acid; chelating agents, likeethylenediaminetetraacetic acid (EDTA); alkanolamines, likeethanolamine; iminosuccinic acid and/or derivatives thereof; salts ofthe aforementioned; and mixtures thereof. The complexing agent accordingto (c) may be present in the conversion solution in a concentrationranging from 5 mmol/l to 5 mol/l, preferably from 50 mmol/l to 3 mol/l,more preferably from 100 mmol/l to 2 mol.

Preferably, the conversion solution is an alkaline solution. Morepreferably, the pH value of the conversion solution ranges from 8 to 15,even more preferably from 10 to 15 and most preferably from 12 to 15.

The temperature of the conversion solution may range from 40° C. to 80°C., preferably from 45° C. to 70° C., when treating the nonconductiveplastic surfaces. The treatment time may range from 1 minute to 20minutes, preferably from 2 minutes to 10 minutes.

The plastic surface which has thus been rendered conductive cansubsequently be further metallized electrolytically, in order to obtaina functional or decorative surface.

In another preferred embodiment of the invention, the plastic surfacesare metallized also by means of direct electroplating. In thisembodiment, the following alternative process step is performed betweenprocess steps A) and B):

A iv) treating the plastic surfaces in a sulfide containing solution.

Preferably, alternative process step A iv) is performed after processsteps A) or A i). This alternative process step A iv) replaces step Aiv) of the embodiment in which the etched plastics surface is metallizedby direct electroplating via treatment with a conversion solution andalternative process step A iv) replaces steps A iv) and A v) of theembodiment in which the etched plastics surface is metallized byelectroless metal plating. Surprisingly, this treatment generates ametal sulfide layer on the plastic surfaces that is sufficientlyelectrically conductive to enable direct electroplating afterwards. Themetal of the generated metal sulfide originates from the etchingsolution containing a source for metal ion according to (iii) applied tothe plastic surface in process step A). If, for example, an etchingsolution containing 10 g/l copper sulfate is used in process step A),the substrate surface is covered with a manganese dioxide layercontaining an amount of about 0.7 g/m² manganese. This manganese dioxidelayer contains copper ions in an amount of about 100 mg/m² copper ions.This amount of copper is sufficient to enable direct electroplating insubsequent process step B).

The plastic surface which has thus been rendered conductive cansubsequently be further metallized electrolytically, in order to obtaina functional or decorative surface.

Thus, in this embodiment it is possible to metallize a nonconductiveplastic surface by performing only three method steps:

-   A) treating the plastic surface with the at least one acidic etching    solution containing metal ions according to (iii) as described    above,-   A iv) treating the plastic surfaces in a sulfide containing    solution, and-   B) metallizing the plastic surface by direct electroplating.

All further process steps described above are not necessary. Inaddition, the deposited metal layer is of good quality and has goodadhesion strength. Thus, the acidic permanganate etching solutioncontaining metal ions according to (iii) is not only excellently stable.It also provides good etching of plastic surfaces which leads to goodadhesion strength of metal layers deposited thereon. It further enablesdirect metallizing of plastic surfaces in only three process steps.

The source for sulfide in the sulfide containing solution is selectedfrom alkali metal sulfides, earth alkali metal sulfides and ammoniumsulfides. The sulfide may be a monosulfide, disulfide, tetrasulfide or apolysulfide. Preferably the source for sulfide in the sulfide containingsolution is selected from sodium monosulfide, sodium disulphide,potassium monosulfide and potassium disulphide. The concentration of thesource for sulphide ranges from 0.5 to 50 g/l, preferably from 0.5 to 10g/l, more preferably from 2 to 8 g/l.

The sulfide containing solution may further be an alkaline solution. ThepH value of the sulfide containing solution ranges from 8 to 12,preferably from 9 to 11. Thus the sulfide containing solution comprisesa source for hydroxide ions. The source for hydroxide ions in thesulfide containing solution is selected from alkali metal hydroxides,earth alkali metal hydroxides and ammonium hydroxide. Preferably thesource for hydroxide ions is selected from sodium hydroxide andpotassium hydroxide. The concentration of the source for hydroxide ionsranges from 1 to 25 g/l, preferably from 5 to 10 g/l.

The treatment with the sulfide solution is performed for a time rangingfrom 1 minute to 10 minutes, preferably from 2 to 7 minutes. Thetreatment with the sulfide solution is performed at a temperatureranging from 20 to 60° C., preferably from 30 to 50° C.

The treatment with the sulfide containing solution has two effects. Itreduces the manganese dioxide deposited on the surface of the plasticsubstrate during process step A). Thus, it removes the manganese dioxideand thereby contributes to the adhesion strength of the subsequentlydeposited metal layer. In addition, the sulfide containing solutionforms an electrically conductive metal sulfide layer with the metal ionsaccording to (iii) originating from the inventive etching solution.Surprisingly, the metal ions according to (iii) are not removed by thesulfide containing solution together with the manganese dioxide althoughthe metal ions are contained within the manganese dioxide layer.Surprisingly, a sufficient amount of metal ions according to (iii)remains on the surface of the plastic substrate to generate a metalsulfide layer with an electrical conductivity sufficient for subsequentdirect electroplating.

In this embodiment, the pretreatment step may be performed prior toprocess step A):

pretreatment step: treating the plastic surface in an aqueous solutioncomprising at least one glycol compound.

This process step is already described above and is performed asdescribed above. This process step is an optional process step; it isnot essential for rendering the plastic surface sufficiently conductiveto enable direct electroplating.

In this embodiment, the process step A i) may be performed after processstep A):

A i) treating the plastic surface with an alkaline etching solution.

This process step is already described above and is performed asdescribed above. Preferably, optional process step A i) is performedbetween process step A) and process step B), more preferably betweenprocess step A) and process step A iv). If alternative process step Aiii) is performed, optional process step A i) is preferably performedbetween process step A) and alternative process step A iii). Processstep A i) is an optional process step; it is not essential for renderingthe plastic surface sufficiently conductive to enable directelectroplating. But if performed, optional process step A i) contributesto improving the adhesion strength of the metal layer subsequentlydeposited onto the nonconductive plastic surface.

In this embodiment, the following alternative process step may beperformed between process steps A) and B):

A iii) treating the plastic surface in a solution containing a sourcefor metal ions.

This alternative process step A iii) replaces step A iii) of theembodiment in which the etched plastics surface is metallized by directelectroplating via treatment with a conversion solution and alternativeprocess step A iii) replaces step A iii) of the embodiment in which theetched plastics surface is metallized by electroless metal plating.

The metal of the metal ion according to A iii) is selected fromtitanium, zirconium, vanadium, niobium, chromium, molybdenum, ruthenium,cobalt, rhodium, nickel, palladium, copper, silver, zinc, bismuth andcadmium. Preferably, the metal is selected from titanium, zirconium,vanadium, niobium, chromium, molybdenum, ruthenium, cobalt, rhodium,nickel, palladium, copper, silver, zinc and cadmium. More preferably,the metal is selected from copper, nickel, zinc, chromium and cobalt.Even more preferably, the metal is copper.

The at least one source for a metal ion according to A iii) is selectedfrom water soluble salts of the above listed metals of the metal ionaccording to A iii). Preferably, the at least one source for a metal ionis selected from water soluble sulphate, phosphate, nitrate andpermanganate salts of the above listed metals of the metal ion. Morepreferably, the at least one source for a metal ion is selected fromcopper sulfate, copper phosphate, copper nitrate, copper permanganate,silver nitrate, zinc sulphate, zinc nitrate, zinc permanganate, cadmiumsulphate, cadmium nitrate, titanium sulfate, titanium nitrate, zirconiumsulfate, vanadyl sulfate, chromium trioxide, chromium(III) trisulfate,chromium(II) sulfate, chromium nitrate, cobalt sulphate, cobalt nitrate,nickel sulfate, nickel nitrate, rhodium sulphate and the hydratesthereof. Most preferably, the at least one source for a metal ion isselected from copper sulfate, copper phosphate, copper nitrate, copperpermanganate and the hydrates thereof. The concentration of the metalion according to A iii) ranges from 1 mmol/l to 1 mol/l, preferably from10 mmol/l to 1 mol/l, more preferably from 10 mmol/l to 100 mmol/l, mostpreferably 30 mmol/l to 100 mmol/l.

The solution containing a source for metal ions according to A iii) canbe employed at temperatures ranging from 20 to 60° C., preferably from30 to 50° C. The treatment with the solution containing a source formetal ions according to A iii) is performed for a time ranging from 1minute to 10 minutes, preferably from 2 to 7 minutes.

The solution containing a source for metal ions according to A iii) maybe an alkaline solution. The pH value may range from 7.5 to 12.5,preferably from 8 to 12. pH adjusting agents are selected from ammoniaand/or amine. Amines may be monoethanolamine and/or triethanolamine.

This alternative process step A iii) is an optional process step; it isnot essential for rendering the plastic surface sufficiently conductiveto enable direct electroplating.

For industrial scale application of metallization of plastic surfaces,the articles are usually fastened to racks. These are metallic carriersystems which allow the simultaneous treatment of a large number ofarticles with the successive solutions for the individual process steps,and last steps for electrolytic deposition of one or more metal layers.The racks are generally themselves coated with plastic, e.g. poly vinylchloride (PVC). Therefore, the racks in principle likewise constitute asubstrate for metallization processes on plastic surfaces. However, theadditional metallization of the racks is undesirable, since the metallayers have to be removed again from the racks after the coating of thearticles. This means additional cost and inconvenience for the removal,combined with additional consumption of chemicals. Moreover, theproductivity of the metallization plant in this case is lower, since theracks first have to be demetallized prior to reloading with articles. Ifthe demetallization has to take place using semi-concentratedhydrochloric acid and/or using nitric acid, vapours and aerosols areproduced, and these lead to corrosion in the environment. A furtherproblem is that, when rack metallization occurs, it is no longerpossible to achieve a defined current density in a reproducible mannerbecause the extent of the rack coverage is usually unknown, and theexact surface area of the rack is likewise unknown. The consequence isthen usually that the metal layer applied to the galvanized plasticarticles is too thin.

In a further embodiment of the invention, rack metallization can beprevented by slipping stripes of a plastic material that is not etchedby the inventive etching solution over the plastic coat of the rack.Preferably, in the embodiment of the invention, containing the processstep of treating the plastic surfaces in a sulfide containing solution,rack metallization can be prevented by slipping stripes of a plasticmaterial that is not etched by the inventive etching solution over theplastic coat of the rack. Preventing rack metallization by this processstep is of particular advantage for the the embodiment containing theprocess step of treating the plastic surfaces in a sulfide containingsolution.

Plastic material not being etched by the inventive etching solution isselected from polytetrafluoroethylene (PTFE), polyvinylidene difluoride(PVDF), copolymers of hexafluoropropylene (HFP) and vinylidene fluoride(VDF or VF2), terpolymers of tetrafluoroethylene (TFE), vinylidenefluoride (VDF) and hexafluoropropylene (HFP) orperfluoromethylvinylether (PMVE) containing elastomers. Further examplesof plastic material not being etched by the inventive etching solutionare terpolymers of TFE, VDF and propylene; as well as fluoroelastomerscomposed of VDF, HFP, TFE, PMVE, and Ethylene. Preferably, the plasticmaterial not being etched by the inventive etching solution may be aheat shrinkable plastic material. Preferably, the stripes of a plasticmaterial not being etched by the inventive etching solution may alsohave the form of a shrinkable tubing, preferably a heat shrinkabletubing.

Stripes of the plastic material not being etched by the inventiveetching solution are slipped over the plastic coat in positions of therack where an electrically conductive layer of metal sulfide would leadto rack metallization. Preferably, these positions are in the very nearof the electrical contacts of the rack. The stripes of the plasticmaterial not being etched by the inventive etching solution are notcovered with an electrically conductive metal sulfide layer. Thereforethey interrupt the electrical contact to the conductive metal sulfidelayer coated over the parts of original plastic coat of the rack andthus prevent metallization of the rack during direct electroplating.

Accordingly, the process step of slipping stripes of a plastic materialnot being etched by the inventive etching solution over the plastic coatof the rack may be performed prior to process step A), preferably priorto the pretreatment step.

Step B) of the process according to the invention is the metallizationof the plastic surface with a metallization solution. The metallizationin process step B) can be effected electrolytically. For electrolyticmetallization, it is possible to use any desired metal deposition baths,for example for deposition of nickel, copper, silver, gold, tin, zinc,iron, lead or alloys thereof. Such deposition baths are familiar tothose skilled in the art. A Watts nickel bath is typically used as abright nickel bath, this comprising nickel sulphate, nickel chloride andboric acid, and also saccharine as an additive. An example of acomposition used as a bright copper bath is one comprising coppersulphate, sulphuric acid, sodium chloride and organic sulphur compoundsin which the sulphur is in a low oxidation state, for example organicsulphides or disulphides, as additives. In particular, electrodepositionbath compositions being weakly acidic to alkaline are suited for theembodiment of the invention containing the process step of treating theplastic surfaces in a sulfide containing solution. The pH value ofelectrodeposition baths suited for this embodiment ranges from 3 to 10.

The effect of the metallization of the plastic surface in process stepB) is that the plastic surface is coated with metal, the metal beingselected from the above-listed metals for the deposition baths.

In a further embodiment of the invention, after process step B), thefollowing further process step is performed:

B i) storage of the metallized plastic surface at elevated temperature.

As in all electroplating processes in which a nonconductor is coated bywet-chemical means with a metal, the adhesion strength between metal andplastic substrate increases in the first period after the application ofthe metal layer. At room temperature, this process is complete afterabout three days. This can be accelerated considerably by storage atelevated temperature.

Such a step may involve treating a metallized article made of ABSplastic at elevated temperature in the range from 50° C. to 80° C. for aperiod between 5 minutes and 60 minutes, preferably at a temperature of70° C. The effect of the treatment or storage of the metallized plasticsurfaces at elevated temperature is that an initial, relatively lowadhesion strength is enhanced further, such that, after process step Bi), an adhesion strength of the metal layer applied to the plasticsurface which is within the desired range of at least or greater than0.6 N/mm is achieved.

The process according to the invention thus enables, with good processreliability and excellent adhesion strength of the subsequently appliedmetal layers, achievement of metallization of electrically nonconductiveplastic surfaces of articles. In this context, not just planar plasticsurfaces are metallized with high adhesion strength by the processaccording to the invention; instead, inhomogeneously shaped plasticsurfaces are also provided with a homogeneous and strongly adhered metalcoating.

EXAMPLES Example 1

In a plating line, ABS/PC—blend parts (Mini Front Finishers made ofBayblend T45PG) were plated. To achieve this, the line comprised thefollowing process steps: a 3901 tank containing a 40% solution ofethyldiglycol acetate at 25±1° C. (pretreatment step for 7 minutes), a525 l tank containing a solution of 100 g/l sodium permanganate and 10g/l sulfuric acid (96%) at 70° C. (comparative acidic etching solutionwithout metal ion according to (iii); etching step instead of inventiveprocess step A) for 10 minutes), a 340 l tank containing a solution madeof 25 ml/l (96%) sulfuric acid and 30 ml/l of 30% hydrogen peroxide(process step A ii) at 40° C.), a pre-dip solution (preliminary dippingstep, 300 ml/l 36% hydrochloric acid at ambient temperature), anactivator bath (process step A iii), colloidal palladium, 40 mg/l, 37°C. for 5 minutes), an accelerator (process step A iv), Adhemax ACC1 ofAtotech at 45° C., for 5 minutes), an electroless nickel bath (processstep A v), Adhemax Ni LFS of Atotech at 40° C. for 10 minutes) followedby a copper electroplating step for 70 minutes (Cupracid HT fromAtotech, 3.5 A/dm2, room temperature; process step B)). Between allsteps two rinses with water were used to clean the plastic surface andprevent from drag-in of a solution into a subsequent process bath.

Every day, 2 m² plastic surface were plated using the described platingline layout. The concentration of the permanganate in the etching stepwas monitored daily using a photometrical method (absorption at 520 nm).Using the result, consumed permanganate was then replenished. During thefirst week of operation, no substantial consumption was found. In thesecond week, about 2.5 kg sodium permanganate were added, 11.5 kg wereadded in the following week, and almost 23 kg in the fifth week of lineoperation.

After the fifth week 20 g/l copper-sulfate pentahydrate were added tothe acidic etching solution to give the composition of the inventiveetching solution containing copper ions as metal ions according to(iii). In the sixth and seventh week of operation, no substantialconsumption of permanganate was found anymore. Nevertheless,ABS/PC—blend parts plated during sixth and seventh week were coveredwith metal completely and with the same high adhesion strength as partsplated during week one to five. Thus, the ABS/PC parts were etched withgood quality by the inventive etching solution and method. Theconsumption of permanganate due to etching was nearly not detectable andconsumption of permanganate due to self-decomposition did not occur inthe inventive etching solution.

Example 2

In an application laboratory, plastic parts of different compositionwere plated: ABS (Novodur P2MC) and ABS-PC-blends (Bayblend T45PG). Two701 tanks were used, containing a 40% solution of ethyldiglycol acetateat 25° C. for ABS-PC, and a solution of 10% butylglycol and 15%ethyldiglycol acetate at 45° C. for the ABS. The ABS-PC parts werepre-treated in its respective solution for 7 minutes and the ABS partswere pre-treated in its respective solution for 10 minutes (pretreatmentstep). A 170 l etching tank contained an acidic permanganate solution(100 g/l sodium permanganate, 10 g/l 96% sulfuric acid, 70° C.). Allplastic parts were treated with the acidic permanganate solution(comparative acidic etching solution without metal ion according to(iii); etching step instead of inventive process step A)) for 10minutes. All further process steps were the same as are alreadydescribed in example 1, just in smaller volumes of 701.

After one week of plating, about 5 kg wet manganese dioxide sludge hadto be removed from the bottom of the etching tank. The sludge influencedthe etching process leading to some skip plating in subsequent processsteps. After cleaning the tank and removing manganese dioxide from thetank walls using acidic hydrogen peroxide solution, the etching solutionwas pumped back into the tank. 20 g/l copper-sulfate pentahydrate wereadded to the acidic etching solution to give the composition of theinventive etching solution containing copper ions as metal ionsaccording to (iii). After one week operation, the inventive acidicetching solution again was pumped out. Only traces of manganese dioxidesludge were found. Thus, the decrease of consumption of permanganateshown in Example 1 is accompanied by a decrease of formation ofmanganese dioxide.

Example 3

In a production line, ABS plastic substrates were plated. To achievethis, a 3500 l tank was filled with a solution of 10% butylglycol and15% ethyldiglycol acetate and held at 45° C. and the substrates treatedtherein (pretreatment step for 10 minutes). After one rinse step withwater, the plastic substrates were treated in a 4800 l tank holding asolution of 100 g/l sodium permanganate and 10 g/l sulfuric acid at 70°C. (comparative acidic etching solution without metal ion according to(iii); etching step instead of inventive process step A)) for 10minutes. This tank was connected to a lamellar clarifier (3501 volume)to separate sludge from the solution. After one rinse, the plasticsubstrates were treated in an alkaline permanganate solution at 60° C.(30 g/l NaMnO4 and 20 g/l NaOH) for 10 minutes; process step A° i)). Theplastic surfaces were then cleaned from manganese dioxide using acidichydrogen peroxide (25 ml/l 96% sulfuric acid and 30 ml/l of 30% hydrogenperoxide at 40° C.; process step A ii)). Subsequently, the plasticsubstrates were preliminarily dipped as specified in Example 1(preliminary dipping step) and activated in a palladium colloid (100mg/l palladium, NeoLink Activator, Atotech product) at 45° C. (processstep A iii)). To obtain an electrically conductive layer of thedeposited palladium colloid, the substrates were dipped into aconversion solution based on copper ions (NeoLink from Atotech, processstep A iv)) for 3 minutes at 55° C. All substrates were copper-plated byintroducing them into a copper electroplating bath (Cupracid Ultra, fromAtotech, process step B)) at 20° C. for 60 minutes and applying 3.5A/dm² of current.

After one week operation and processing of only 3 m² plastic surface,about 30 kg manganese dioxide sludge were separated by the lamellarclarifier.

After the first week, 20 g/l copper-sulfate pentahydrate were added tothe acidic etching solution to give the composition of the inventiveetching solution containing copper ions as metal ions according to(iii). In the following week about 15 m² ABS plastic substrates wereetched. After this week, only traces of manganese dioxide sludge werefound.

Example 4

As shown by the preceding examples, permanganate of the inventive acidicetching solution is predominantly consumed for etching the surfaces ofthe plastic substrates. As a result, manganese dioxide is formed whichseparates into the etching solution. In the presence of acid manganesedioxide catalyzes the oxidation of water, producing more manganesedioxide. In this process, oxygen is liberated. Therefore, the evolvedoxygen is an indicator for the decomposition reaction of permanganate.

A round bottomed glass flask with a total volume of about one liter wasclosed with a glass stopper having an outlet for evolved gas. A silicontube from the outlet lead into a water bath where a graduated glasscylinder filled with water was placed upside-down to collect all gasevolved. The round bottomed flask was placed in a beaker with water heldat 70° C. Exactly 600 ml of a pre-heated permanganate solution (100 g/lsodium permanganate, 10 g/l 96% sulfuric acid) were placed into theglass flask. In this permanganate solution, 3 dm² of pre-treated ABSplastic substrate were previously etched for ten minutes (comparativeacidic etching solution without metal ion according to (iii); etchingstep instead of inventive process step A)). The substrate was removedfrom the permanganate solution. The stopper was applied to the flask,and after allowing some minutes for adjusting temperatures, the evolvedgas was collected.

The amounts of oxygen collected during specific time intervals aresummarized in Table 1 and the data of the first trial are shown in FIG.1.

The trial was repeated. This time the acidic permanganate solutioncontained 10 g/l copper sulfate pentahydrate and thus corresponded tothe inventive etching solution containing copper ions as metal ionsaccording to (iii). The amounts of oxygen collected during specific timeintervals are summarized in Table 2 and the data of the first trial areshown in FIG. 2.

In the comparative acidic permanganate solution the oxygen evolutionsteadily continued and the amount of oxygen generated was significantlyhigher than in the inventive acidic permanganate solution containingmetal ions according to (iii). In addition, the evolution of oxygenapproached a threshold value in the inventive permanganate solution.Thus, after some time the gas evolution ceased in the inventivepermanganate solution.

TABLE 1 Oxygen evolution in acidic permanganate solution without metalion according to (iii) Duration [min] 0 10 32 55 85 123 166 200 260 320Oxygen 0 7 20 27 32 41 48 55 65 74 [ml]

TABLE 2 Oxygen evolution in acidic permanganate solution with metal ionaccording to (iii) Duration [min] 0 22 45 75 100 150 195 255 320 Oxygen5 13 21 23 28 29 29 31 32 [ml]

Example 5

Adhesion Strength of Metal Layers Deposited on Etched Plastic Surfaces

Four ABS/PC—blend parts (Mini Front Finishers made of Bayblend T45PG)were dipped for 7 minutes into a solution of 40% solution ofethyldiglycol acetate at 25±1° C. (pretreatment step). All parts wererinsed under running water for one minute. Subsequently, parts 1 and 3were introduced into a bath of 100 g/l sodium permanganate and 10 g/l96% sulphuric acid (comparative acidic etching solution without metalion according to (iii); etching step instead of inventive process stepA)) for 10 minutes. Meanwhile, parts 2 and 4 were immersed in an a bathof 100 g/l sodium permanganate, 10 g/l 96% sulphuric acid and 20 g/lcopper-sulfate pentahydrate, which was kept at 70° C. (inventive acidicetching solution; process step A)). Afterwards parts 3 and 4 weresubjected to a further etching in alkaline permanganate solution at 60°C. (30 g/l NaMnO₄ and 20 g/l NaOH) for 10 minutes; process step A°i)).

Then all parts were cleaned to remove deposited manganese dioxide in asolution of 50 g/l 96% sulphuric acid and 30 ml/l 30% hydrogen peroxide(process step A ii)). After brief dipping into a solution of 300 ml/l36% hydrochloric acid (process step preliminary dipping), the parts 1and 2 were activated in a colloidal activator based on a palladiumcolloid (Adhemax Aktivator PL from Atotech, 25 ppm of palladium) at 45°C. for three minutes (process step A° iii)). Parts 3 and 4 wereactivated in the same way (Adhemax Aktivator PL from Atotech, 100 ppm ofpalladium).

From parts 1 and 2 the protective shells of the palladium particles wereremoved at 50° C. for five minutes (Adhemax ACC1 accelerator fromAtotech, process step A°iv)). Parts 1 and 2 were subsequentlynickel-plated at 45° C. without external current for ten minutes(Adhemax LFS, from Atotech, process step A°v)) and rinsed.

To obtain an electrically conductive layer of the deposited palladiumcolloid, parts 3 and 4 were dipped into a conversion solution based oncopper ions (NeoLink from Atotech, process step A iv)) for 3 minutes at55° C.

All parts were copper-plated by introducing them into a copperelectroplating bath (Cupracid Ultra, from Atotech, process step B)) at20° C. for 60 minutes and applying 3.5 A/dm² of current.

All parts were stored at 80° C. for 30 minutes (process step B i)).Subsequently, a knife was used to cut out a strip of the metallizedplastic panel of a width of about 1 cm, and a tensile tester (fromInstron) was used to pull the metal layer away from the plastic (ASTM B533 1985 Reapproved 2009). The adhesion strengths obtained aresummarized in Table 3.

TABLE 3 Adhesion strength of metal layers deposited on plastic surfacesdifferently etched Metal Adhesion Permanganate ions according strengthetching solution Metallizing to (iii) [N/mm] Acidic 1. Electrolessdeposition without 1.21 2. Electrodeposition with 1.11 1. Acidic Directelectrodeposition without 1.25 2. Alkaline with 1.18

Example 6

A panel made of ABS (Novodur P2MC) with dimensions of 15 cm×5 cm×0.3 cmwas dipped into a solution of 15% diethylene glycol ethylether acetateand 10% ethylene glycolmonobutylether at 45° C. for 10 minutes(pretreatment step). The solution had been adjusted to pH 7 with apotassium phosphate buffer. The panel was rinsed with cold water andafterwards immersed in a bath of 100 g/l sodium permanganate and 10 g/l96% sulphuric acid and 10 g/l copper sulphate pentahydrate, which waskept at 70° C. (inventive acidic etching solution; process step A)) for10 minutes. After a further rinsing step, the panel was dipped into asolution of 5 g/l sodium sulfide at 40° C. for 3 minutes in order toobtain an electrically conductive layer (process step A iv)). The colourof the panel surface changed from dark brown to beige yellow.Subsequently, the panel was subjected to a Watts nickel electroplatingbath and electrically connected with an electrical current source.Voltage between the panel and an anode was adjusted to 3.5 V. The panelwas electroplated with nickel for 6 minutes (process step B)) andrinsed. Afterwards, the panel was electroplated with copper in an acidiccopper bath (Cupracid 210, product of Atotech Deutschland GmbH) at 20°C. for 60 minutes by applying 3.5 A/dm² of current (process step B)).The nickel layer and copper layer completely covered the panel surfaceand had no defects.

Example 7

Example 6 was repeated using a panel made of ABS/PC (Bayblend T45)having the same dimensions as the panel used in Example 6. Afterdeposition of the copper layer, the ABS/PC panel was stored at 70° C.for 60 minutes (process step B i)). Subsequently, the adhesion strengthof the deposited layer stack of nickel and copper was measured asdescribed in Example 5. The adhesion strength was between 0.7 and 0.9N/mm.

Example 8

A panel made of ABS (Polylac 727, product of Chi Mei Corp.) withdimensions of 15 cm×5 cm×0.3 cm was dipped into a solution of 40 vol %diethylene glycol ethylether acetate at 22° C. for 10 minutes(pretreatment step). Afterwards, the panel was treated with a sulfidesolution and electroplated with nickel and copper as described inExample 6. Subsequently, the adhesion strength of the deposited layerstack of nickel and copper was measured as described in Example 5. Theadhesion strength was between 0.8 and 1.1 N/mm.

Example 9

Parts of a tubing made of a copolymer of HFP and VDF (Viton, product ofDuPont) were slipped over the contacts of a PVC-coated holding rack(process step prior to pretreatment step). The tubing covered the jointsbetween the metallic contacts and the PVC coat. The part of the metalliccontacts used for fastening the articles to be plated were left free ofthe tubing. The tubing parts had a length of about 5 mm. For thisexample, an old holding rack having a particularly strong tendency torack metallization was selected. An ABS moulding was fastened to thecontacts of the holding rack. The moulding and the rack were treated asdescribed in Example 6. The ABS moulding was completely covered with anickel layer and a copper layer without any defects, while the rack wasfree of any metal deposit.

Example 10

Four ABS mouldings (valve caps made of Polylac 727, product of ShimeiCorp.) were dipped into a solution of 15% diethylene glycol ethyletheracetate and 10% ethylene glycolmonobutylether at 45° C. for 2 minutes(pretreatment step). The solution had been adjusted to pH 7 with apotassium phosphate buffer. Afterwards, the mouldings were rinsedthoroughly with cold water.

The mouldings (1 to 4) were immersed in solutions according to theinvention (process step A)) being composed of 10 g/l 96% sulphuric acid,20 g/l copper-sulfate pentahydrate and varying concentrations of sodiumpermanganate (see Table 4). The inventive etching solutions had atemperature of 70° C. Mouldings 1 to 4 were treated with the inventiveetching solutions for 10 minutes.

Afterwards, the mouldings were cleaned to remove deposited manganesedioxide in a solution of 50 g/l 96% sulphuric acid and 30 ml/l 30%hydrogen peroxide (process step A ii)). After brief dipping into asolution of 300 ml/l 36% hydrochloric acid (process step preliminarydipping), the mouldings were activated in a colloidal activator based ona palladium colloid (Adhemax Aktivator PL from Atotech, 25 ppm ofpalladium) at 45° C. for five minutes (process step A° iii)). Theprotective shells of the palladium particles were removed at 40° C. forfive minutes (Adhemax ACC1 accelerator from Atotech, process step A°iv)). The mouldings were subsequently nickel-plated at 40° C. withoutexternal current for ten minutes (Adhemax LFS, from Atotech, processstep A°v)) and rinsed. Subsequently, the mouldings were copper-plated byintroducing them into a copper electroplating bath (Cupracid 5000, fromAtotech, process step B)) at 25° C. for 60 minutes and applying 4 A/dm²of current.

The mouldings were stored at 80° C. for 30 minutes (process step B i)).Then, the adhesion strength of the deposited metal layer was measured asdescribed in Example 5. The adhesion strengths obtained are summarizedin Table 4.

TABLE 4 Adhesion strength of metal layers deposited on plastic surfacesdifferently etched Permanganate concentration [g/l] Adhesion strength[N/mm] 10 1.59 20 2.07 30 2.17

Example 11

Amounts of oxygen generated in acidic permanganate solutions withvarying permanganate concentrations were measured as described inExample 4 in absence and presence of metal ions according to (iii).Concentrations of components of the permanganate solutions andmeasurement results are summarized in Table 5 and shown in FIG. 3.

TABLE 5 Oxygen evolution in acidic permanganate solution in absence andpresence of metal ion according to (iii) Time [min] 0 5 10 15 25 30 4560 75 90 105 120 5 g/l NaMnO₄, 10 g/l 96% H₂SO₄ Oxygen 0 12 — 23 — 28 3336 39 41 41 43 [ml] 5 g/l NaMnO₄, 10 g/l 96% H₂SO₄, 20 g/l CuSO₄ × 5 H₂OOxygen 0 — —  6 — 13 13 13 13 — — — [ml] 10 g/l NaMnO₄, 10 g/l 96% H₂SO₄Oxygen 0 — — 13 — 18 20 26 32 32 32 32 [ml] 10 g/l NaMnO₄, 10 g/l 96%H₂SO₄, 20 g/l CuSO₄ × 5 H₂O Oxygen 0 — —  0 —  0  0  0  0  0  0  0 [ml]30 g/l NaMnO₄, 10 g/l 96% H₂SO₄ Oxygen 0 — 5 12 14 — 20 21 22 26 32 —[ml] 30 g/l NaMnO₄, 10 g/l 96% H₂SO₄, 12 g/l CuSO₄ × 5 H₂O Oxygen 0 — 811 — 13 13 13 — — — — [ml] “—” means: not measured.

Example 12

Amounts of oxygen generated in acidic permanganate solutions weremeasured as described in Example 4 in absence and presence of metal ionsaccording to (iii) (according to invention) and in presence of metalions different from metal ions according to (iii) (comparative).Concentrations of components of the permanganate solutions andmeasurement results are summarized in Table 6 and shown in FIG. 4.

TABLE 6 Oxygen evolution in acidic permanganate solution in absence andpresence of metal ion according to (iii) 100 g/l NaMnO₄, 10 g/l 96%H₂SO₄ Time [min] 0 10 25 55 85 125 200 260 Oxygen 0 7 20 27 32 41 55 65[ml] 100 g/l NaMnO₄, 10 g/l 96% H₂SO₄, 10 g/l CuSO₄ × 5 H₂O Time [min] 010 30 50 60 140 200 240 Oxygen 0 21 24 26 26 29 30 30 [ml] 100 g/lNaMnO₄, 10 g/l 96% H₂SO₄, 20 g/l CuSO₄ × 5 H₂O Time [min] 0 10 25 70 90120 180 240 Oxygen 0 19 22 23 24 24 25 25 [ml] 100 g/l NaMnO₄, 10 g/l96% H₂SO₄, 3 g/l NaVO₃ Time [min] 0 5 10 15 20 25 32 40 45 60 Oxygen 0 310 15 18 22 28 34 37 42 [ml] 100 g/l NaMnO₄, 10 g/l 96% H₂SO₄, 20 g/lCoSO₄ × 7 H₂O Time [min] 0 5 15 20 40 60 90 110 135 180 210 240 Oxygen 07 20 36 50 70 100 125 155 197 230 270 [ml] 100 g/l NaMnO₄, 10 g/l 96%H₂SO₄, 10 g/l CrO₃ Time [min] 0 20 45 60 Oxygen 0 23 63 85 [ml] 100 g/lNaMnO₄, 10 g/l 96% H₂SO₄, 10 g/l Fe₂(SO₄)₃ × 9 H₂O Time [min] 0 10 15 2030 40 45 Oxygen 0 36 72 99 147 181 200 [ml] “—” means: not measured.

16.2 g/l palladium(II)sulfate were added to a solution composed of 100g/l sodium permanganate and 10 g/l 96% sulphuric acid. Thereupon, thesolution decomposed nearly explosively.

The invention claimed is:
 1. Etching solution for treating nonconductiveplastic surfaces, comprising (i) at least one acid, wherein theconcentration of the at least one acid ranges from 0.02-0.6 mol/l basedon a monobasic acid; and (ii) at least one permanganate salt selectedfrom alkali metal permanganates and earth alkali metal permanganates,wherein the permanganate salt is present in the etching solution in aconcentration between 30 g/l and 250 g/l; and (iii) at least one sourcefor a metal ion, wherein the metal of the metal ion is selected fromtitanium, zirconium, niobium, molybdenum, ruthenium, rhodium, nickel,copper, silver, zinc and cadmium, characterized in that the molar ratioof permanganate ions according to (ii) to metal ions according to (iii)ranges from 8.75:1 to 40:1.
 2. The etching solution according to claim1, characterized in that the metal of the metal ion according to (iii)is copper.
 3. The etching solution according to claim 1, characterizedin that the concentration of the metal ion according to (iii) rangesfrom 1 mmol/l to 1 mol/l.
 4. The etching solution according to claim 1,characterized in that the molar ratio of permanganate ions according to(ii) to metal ions according to (iii) ranges from 10:1 to 40:1.
 5. Theetching solution according to claim 1, characterized in that the molarratio of permanganate ions according to (ii) to metal ions according to(iii) ranges from 10:1 to 20:1.